D. H. Lawrence, Studies in Classic American Literature (NY: Penguin, 1977) -- orig. 1923. Especially Ch. 2.
Faÿ, Bernard, Franklin, The Apostle of Modern Times (Boston: Little, Brown, & Co., 1929), First Printing. So far I've read half of the 500 pages and Faÿ gives some helpful background information but not much synthesis. He puts Franklin's reminiscences, in late letters, in their proper earlier places. Adds mention of the Masons, which Franklin mostly leaves out. Good explanation of the Quakers (doves) vs. the hawks in the French & Indian War, which controversy seems to have taken Franklin to England in 1757. Explanations of the events regarding the "wagons" help us understand why Franklin dwells on this so long in the Autobiography--it was truly a very important turning point in his adult life.
Franklin Institute, Meet Dr. Franklin (Lancaster, PA: Lancaster Press, 1943). Collection of essays.
Handlin, Oscar, The Americans (Boston: Little, Brown, 1963).
J. A. Leo Lemay has a good article on the textual elements and rhetorical strategies of "Polly Baker" (help to those writing the paper for R. Lerner's class).
Lokken, Roy, I. Bernard Cohen, and Bowen Dees, eds., Meet Dr. Franklin (Philadelphia: Franklin Institute Press, 1981), reprints several essays from 1943 and adds many more.